The thyroid gland is located in the anterior part of the neck, below the thyroid cartilage and on either side of the trachea, and is divided into two lobes, the right and left, which are connected by an isthmus. The isthmus sometimes extends upward to a vertebral lobe that can be connected to the hyoid bone. The thyroid gland is covered by two layers of peritoneum: the inner layer is the intrinsic thyroid peritoneum and the outer layer is the surgical peritoneum. The thyroid gland is fixed to the trachea and cricoid cartilage by the surgical peritoneum, and is also attached to the cricoid cartilage by the suspensory ligaments at the upper level of the left and right lobes. Therefore, when swallowing, the thyroid gland also moves up and down with it. The parathyroid glands are attached to the back of the thyroid gland between the two layers of the peritoneum. The thyroid gland is rich in blood flow, mainly from the superior and inferior thyroid arteries. The main thyroid veins are the superior middle and inferior thyroid veins. The superior middle vein flows back into the internal jugular vein, and the inferior vein flows back into the innominate vein. The nerve supply to the thyroid gland comes from the fibers of the sympathetic nerves in the middle and lower jugular. During thyroid surgery, the main nerve trunks nearby are often involved, such as the recurrent laryngeal nerve, which runs in the groove between the trachea and esophagus and often intersects with the inferior thyroid artery, and the superior laryngeal nerve, which is often parallel to and close to the superior thyroid artery. If inadvertently mistakenly injured will cause difficulty in pronunciation or misopharynx. The synthesis and secretion of thyroid hormone are controlled and regulated by the cortical hypothalamus and anterior pituitary system. When thyroid hormone is secreted in excess, the secretion of thyroid stimulating hormone can be suppressed. Conversely, when thyroid hormone biosynthesis is impaired, the secretion of thyroid stimulating hormone can be increased. This “feedback effect” maintains the dynamic balance between the hypothalamus, the anterior pituitary and the thyroid gland.